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83 lines
2.9 KiB
Plaintext
83 lines
2.9 KiB
Plaintext
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namespace Eigen {
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/** \eigenManualPage TutorialReshape Reshape
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Since the version 3.4, %Eigen exposes convenient methods to reshape a matrix to another matrix of different sizes or vector.
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All cases are handled via the DenseBase::reshaped(NRowsType,NColsType) and DenseBase::reshaped() functions.
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Those functions do not perform in-place reshaping, but instead return a <i> view </i> on the input expression.
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\eigenAutoToc
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\section TutorialReshapeMat2Mat Reshaped 2D views
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The more general reshaping transformation is handled via: `reshaped(nrows,ncols)`.
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Here is an example reshaping a 4x4 matrix to a 2x8 one:
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<table class="example">
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<tr><th>Example:</th><th>Output:</th></tr>
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<tr><td>
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\include MatrixBase_reshaped_int_int.cpp
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</td>
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<td>
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\verbinclude MatrixBase_reshaped_int_int.out
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</td></tr></table>
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By default, the input coefficients are always interpreted in column-major order regardless of the storage order of the input expression.
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For more control on ordering, compile-time sizes, and automatic size deduction, please see de documentation of DenseBase::reshaped(NRowsType,NColsType) that contains all the details with many examples.
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\section TutorialReshapeMat2Vec 1D linear views
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A very common usage of reshaping is to create a 1D linear view over a given 2D matrix or expression.
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In this case, sizes can be deduced and thus omitted as in the following example:
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<table class="example">
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<tr><th>Example:</th></tr>
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<tr><td>
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\include MatrixBase_reshaped_to_vector.cpp
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</td></tr>
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<tr><th>Output:</th></tr>
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<tr><td>
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\verbinclude MatrixBase_reshaped_to_vector.out
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</td></tr></table>
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This shortcut always returns a column vector and by default input coefficients are always interpreted in column-major order.
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Again, see the documentation of DenseBase::reshaped() for more control on the ordering.
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\section TutorialReshapeInPlace
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The above examples create reshaped views, but what about reshaping inplace a given matrix?
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Of course this task in only conceivable for matrix and arrays having runtime dimensions.
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In many cases, this can be accomplished via PlainObjectBase::resize(Index,Index):
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<table class="example">
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<tr><th>Example:</th></tr>
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<tr><td>
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\include Tutorial_reshaped_vs_resize_1.cpp
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</td></tr>
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<tr><th>Output:</th></tr>
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<tr><td>
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\verbinclude Tutorial_reshaped_vs_resize_1.out
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</td></tr></table>
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However beware that unlike \c reshaped, the result of \c resize depends on the input storage order.
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It thus behaves similarly to `reshaped<AutoOrder>`:
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<table class="example">
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<tr><th>Example:</th></tr>
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<tr><td>
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\include Tutorial_reshaped_vs_resize_2.cpp
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</td></tr>
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<tr><th>Output:</th></tr>
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<tr><td>
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\verbinclude Tutorial_reshaped_vs_resize_2.out
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</td></tr></table>
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Finally, assigning a reshaped matrix to itself is currently not supported and will result to undefined-behavior because of \link TopicAliasing aliasing \endlink.
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The following is forbidden: \code A = A.reshaped(2,8); \endcode
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This is OK: \code A = A.reshaped(2,8).eval(); \endcode
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*/
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}
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